In the Gila Valley compounds, as Casa Grande, and on the Little Colorado, the unit type is unknown. Several blocks of buildings on the Gila are surrounded by a rectangular wall which is wanting in ruins of the Little Colorado and its tributaries. Here one of the units may be enlarged, following in some respects the conditions at Aztec Spring Ruin. A surrounding wall also appears in some of the Pueblo villages and pueblos, but when we compare one of the units of a Casa Grande compound with that of a Montezuma Valley village, we find little in common, the main difference, so far as form is concerned, being the absence of a circular kiva.[57] There is nothing in a Gila Valley compound we can structurally call a circular kiva, and no morphological equivalent of the circular kiva in ruins on the tributaries of the Salt and Gila. On the horizon of the Gila culture area there are no circular kivas, due to acculturation. There are rooms analogous to kivas used for ceremonials at Hopi and Zuñi, but they are not true kivas as we have interpreted them in the San Juan area. Both Hopi and Zuñi are composite people and have elements derived from Gila and Pueblo influences, but neither belong to the pure type in the sense the author defines it. [56] The likeness of the Mesa Verde cliff-houses to the pueblos of Chaco Canyon was long ago suggested by Nordenskiöld. The excavation of Far View House proved that suggestion to be true. [57] This subject is treated at length in my report on Casa Grande in the Twenty-eighth Annual Report of the Bureau of American Ethnology. The author has attempted to show that the structure of the houses whose clustering composes villages in the Montezuma Valley is the same as that of Far View House of the Mummy Lake village on top of Mesa Verde; and that these architectural resemblances are close enough to indicate that the villages of the two localities were inhabited by people of the same general culture. He has proved that the pure type of such a village as shown in Far View House was constructed on the same plan as a cliff-dwelling, notwithstanding one is built in the open, the other in a cave. The geographic extension of this type has been traced into Utah. Ruined pueblos on the Chaco Canyon or at Aztec on the Animas, which is geographically nearer the Mesa Verde, are more concentrated but indicate the same culture. Renewed research is necessary to determine the southern and western extension of the pure type; the northern and eastern horizon is fairly well known.